Nowadays, electronic circuit boards are employed in a variety of products, and they are improving in performance day by day. The frequencies to be used on the circuit boards are also increasing, and accordingly, the flip-chip mounting that ensures low impedance is the appropriate mounting method suitable for electronic devices that use high frequencies. In accordance with an increase in number of portable devices, the flip-chip mounting for mounting IC chips in the bare chip form, not in the package form, on a circuit board is needed. For this reason, the IC chips that are singly mounted on circuit boards and IC chips mounted on electronic devices and flat panel display units include a certain number of defectives. Besides the above-mentioned flip-chip components, an increasing number of components of CSP (Chip Size Package), BGA (Ball Grid Array), and the like have come to be used.
As a conventional method (first prior art example) for bonding an IC chip to the circuit board of an electronic device, there is the one disclosed in Japanese Examined Patent Publication No. 06-66355. This is shown in FIG. 13. As shown in FIG. 13, there is generally known the method for transferring Ag paste 74 onto bumps 73 formed on an IC chip 71, connecting the Ag paste 74 to electrodes 75 of a circuit board 76, thereafter hardening the Ag paste 74 and then pouring an encapsulation material 78 in a space between the IC chip 71 and the circuit board 76.
As a method (second prior art example) for bonding an IC chip to a liquid crystal display, there is generally known a semiconductor chip connecting structure that uses an anisotropic conductive film 80 as disclosed in Japanese Examined Patent Publication No. 62-6652 shown in FIGS. 14A–14B. In such structure, an anisotropic conductive adhesive layer 81 constructed by incorporating conductive particles 82 into an insulative resin 83 is peeled off a separator 85 and coated on a substrate or a glass plate of a liquid crystal display 84. By thermocompression bonding an IC chip 86, the anisotropic conductive adhesive layer 81 is interposed between the lower surface of the IC chip 86 and substrate 84 except for portions below Au bumps 87.
As a third prior art example, there is known a method for coating a UV hardening resin on a substrate, mounting an IC chip on the substrate and applying ultraviolet rays to the resin with pressure, thereby hardening the resin between the IC chip and the substrate and maintaining contact between the two by the shrinkage force of the resin.
As described above, the bonding of an IC chip has been performed by die-bonding an IC chip such as a flat package onto a lead frame, connecting the electrodes of the IC chip to the lead frame by wire-bonding, forming a package by resin molding, thereafter printing solder paste on a circuit board, mounting the flat package IC on the board, and performing reflow of the paste. According to the above processing method called SMT (Surface Mount Technology), it has been difficult to reduce the circuit board size due to a long process and much time consumed for production. For example, an IC chip occupies an area about four times that of the IC chip when encapsulated in a flat package, and this has been a factor for hindering the reduction in size.
In contrast to this, the flip chip processing method of directly mounting an IC chip in bare chip form has come to be more frequently used lately for the achievement of a reduction of processing and a small-size light-weight structure. This flip chip processing method has been developed with many forms such as stud bump bonding (SBB) for executing bump formation on an IC chip, bump leveling, Ag.Pd paste transfer, mounting, inspection, encapsulation with encapsulation resin, and inspection and UV resin bonding for simultaneously executing bump formation on an IC chip and UV hardening resin coating on the board and thereafter executing mounting, UV hardening of the resin, and inspection.
However, each of such methods has had the drawback that much time is taken for the hardening of the paste for connecting the bumps of the IC chip with the electrodes of the board and for the coating and hardening of the encapsulation resin, leading to degraded productivity. It is further required to use ceramic or glass for the circuit board, and this has disadvantageously led to a high cost. According to the method for using conductive paste as in the first prior art example as a bonding material, the bumps of the IC chip have been required to be subjected to leveling so as to be flattened before use, in order to stabilize the transfer mount.
For the bonding structure using the anisotropic conductive adhesive as in the second prior art example, a structure that uses glass as a base material of the circuit board is developed. However, it is difficult to uniformly disperse the conductive particles in the conductive adhesive, and this has caused shortcircuits due to abnormal dispersion of the particles and led to the expense of the conductive adhesive.
The bonding method using the UV hardening resin as in the third prior art example has had the problem that the variation in height of the bumps must be suppressed within ±1 (μm) and the issue that the method cannot achieve connection to a board having a degraded flatness such as a resin board (glass epoxy board). The method using solder has been required to pour and harden the encapsulation resin for alleviating the difference between thermal expansion and contraction of the board and the IC chip after the bonding. This resin encapsulation needs two to four hours, and this has led to the issue that the productivity is significantly low.
In view of the aforementioned conventional issues, the present invention has an object to provide a method and apparatus for mounting an IC chip on a circuit board, intended for bonding the IC chip to the board with high productivity and high reliability necessitating neither the resin encapsulation process for pouring resin in the space between the IC chip and the board after the bonding of the IC chip to the circuit board nor the bump leveling process for adjusting the bump height constant.
Also, in view of the aforementioned conventional issues, the present invention has another object to provide a method and apparatus for mounting an electronic component on a circuit board, intended for directly bonding the electronic component on the circuit board with high productivity.